1. Field of the Invention
This invention relates to a manufacturing method of a phase-shift mask, a method of making a resist pattern and a manufacturing method of a semiconductor device, which are particularly suitable for use when manufacturing a so-called Levenson phase-shift mask, making a resist pattern using a Levenson phase-shift and manufacturing a semiconductor device, which makes a resist pattern by exposure using a Levenson phase-shift mask.
2. Description of Related Art
The lithography process used when manufacturing a semiconductor device, for example, is required to have a high resolution beyond the resolution limit determined by the wavelength of light used for exposure along with progressive miniaturization of patterns.
Recently, for the purpose of enabling fabrication of micro patterns as small as or smaller than the exposure wavelength, a technique has been developed, which uses a high-resolution exposure photo mask called a phase-shift mask, having the function of modulating the phase of transmission light and improving the resolution utilizing interference of light. There are some kinds of such phase-shift masks, e.g., Levenson-type masks, in which light passing mask apertures corresponding to adjacent mask patterns are opposite in phase, and half-tone-type masks whose light shielding portions have a permeability and in which light through the shielding portion is opposite in phase from light passing though a mask aperture. Among those, Levenson phase-shift masks have been used practically for manufacturing DRAM, high-speed LSI, and others, and they have been confirmed to be useful.
Levenson phase-shift masks are generally classified into substrate-excavation-type masks made by excavating a quartz substrate as the mask substrate to ensure that light transmitting mask apertures corresponding to adjacent mask patterns are opposite in phase, and phase-shifter-added-type masks using a phase shifter formed on a quartz substrate.
As one of the substrate-excavation-type Levenson phase-shift mask structures, there is a dual-trench structure. In the dual-trench structure, both of the regions where light passing therethrough becomes opposite in phase, namely, 0xc2x0 and 180xc2x0, are excavated because, by excavating both regions of 0xc2x0 and 180xc2x0 in phase, the difference of contrast between transmission light having the phase of 0xc2x0 and transmission light having the phase of 180xc2x0 is small, and deviation upon pattern transfer can be prevented. A specific example of the substrate-excavation-type Levenson phase-shift mask structure is shown in FIG. 1. In FIG. 1, reference numeral 101 denotes a quartz substrate, 102 is a mask pattern, and 103 and 104 are excavated portions.
FIGS. 2. and 3 show specific examples of the phase-shifter-added-type Levenson phase-shift mask structure. FIG. 2 shows an overlying phase-shifter-added-type; and, FIG. 3 shows an underlying phase-shifter-added-type. In FIGS. 2 and 3, reference numeral 201 denotes a quartz substrate, 202 is a mask pattern, and 203 is the phase shifter.
In case of conducting exposure using the conventional Levenson phase-shift mask, transmission light with the phase of 0xc2x0 and transmission light with the phase of 180xc2x0 are different from each other in variation in contrast caused by the deviation of focal points (defocusing) that occurs upon exposure, and transfer displacement of the pattern occurs due to defocusing. Although a certain degree of defocusing may inevitably occur because of unevenness of the wafer surface for transferring the pattern to, various errors in the exposure device, manufacturing errors of the mask (for example, etching error produced upon excavation of the substrate), and so on, it is important to minimize pattern transfer displacement within an expected defocusing region.
Heretofore, however, no concrete measure for minimizing transfer displacement of the pattern has been proposed.
It is, therefore, an object of the invention to provide a manufacturing method of a phase-shift mask, capable of minimizing the displacement of a transfer pattern while ensuring a lithography process tolerance when conducting exposure by using the phase-shift mask, and thereby capable of improving the transfer positional accuracy. Another subject of the invention to provide a method of making a resist pattern by exposure using the phase-shift mask, and a manufacturing method of a semiconductor device made by forming the resist pattern by exposure using the phase-shift mask.
According to the invention, there is provided a manufacturing method of a phase-shift mask, comprising:
seeking the relationship of optical conditions of an exposure optical system used for exposure and a mask structure with displacement of a pattern to be transferred by exposure; finding the optical conditions and the mask structure that can limit displacement of the pattern within a required range, taking manufacturing errors of the mask into consideration; examining the optical conditions and the mask structure obtained determine whether they ensure a required exposure tolerance and a required focal depth; and
executing fabrication of such a mask to obtain the mask structure when the result of the examination is acceptable.
According to the invention, there is further provided a method of making a resist pattern through exposure using a phase-shift mask, comprising:
seeking the relationship of optical conditions of an exposure optical system used for exposure and a mask structure of the phase-shift mask with displacement of a pattern to be transferred by exposure;
finding the optical conditions and the mask structure that can limit displacement of the pattern within a required range, taking manufacturing errors of the mask into consideration; examining the optical conditions and the mask structure obtained to determine whether they ensure a required exposure tolerance and a required focal depth; and
when the result of the examination is acceptable, fixing the exposure optical system to the optical conditions selected, then actually manufacturing the phase-shift mask having the mask structure selected, and conducting exposure using the exposure optical system and the phase-shift mask.
According to the invention, there is further provided a manufacturing method of a semiconductor device having a step of making a resist pattern through exposure using a phase-shift mask;
seeking the relationship of optical conditions of an exposure optical system used for exposure and a mask structure of the phase-shift mask with displacement of a pattern to be transferred by exposure;
finding the optical conditions and the mask structure that can limit displacement of the pattern within a required range, taking manufacturing errors of the mask into consideration; examining the optical conditions and the mask structure obtained to determine whether they ensure a required exposure tolerance and a required focal depth; and
when the result of the examination is acceptable, fixing the exposure optical system to the optical conditions selected, then actually manufacturing the phase-shift mask having the mask structure selected, and conducting exposure using the exposure optical system and the phase-shift mask.
The process of determining optical conditions of an exposure optical system and a mask structure in the present invention is outlined in the flowchart of FIG. 4.
Representative optical conditions of the exposure optical system are numerical aperture (NA) and partial coherence factor ("sgr"). In exposure devices, in general, the value obtained by dividing the numerical aperture of an illumination optical system by the numerical aperture of the mask side of the projection optical system is called coherence. An intermediate value of such coherence (partial coherent illumination) between its value 0 (coherent illumination) and its value ∞ (incoherent illumination) is herein called the partial coherence factor.
The phase-shift mask is typically a Levenson phase-shift mask of any type of the substrate-excavation-type, as shown in FIG. 1, or of the phase-shifter-added-type, as shown in FIGS. 2 and 3. The mask structure in the former substrate-excavation-type Levenson phase-shift mask is regulated by the amount of excavation of the substrate, and displacement of the transfer pattern is minimized by optimizing the substrate excavation amount. The mask structure in the latter phase shifter-added Levenson phase-shift mask is regulated by the thickness of the phase shifter, and displacement of the transfer pattern is minimized by optimizing the thickness of the phase shifter.
In the case of the simplest pattern, like a uniform pattern in which a unit pattern is regularly arranged in equal intervals, determination of a pattern employed in FIG. 4 is determined by its design rule. On the other hand, in the case of a complicated, non-uniform pattern, like logical LSI, etc., the width and shape of the excavation, in case of a substrate-excavation-type Levenson phase-shift mask, or width and shape of the phase shifter, in case of a phase shifter-added Levenson phase-shift mask, also become complicated, and therefore, displacement of the transfer pattern and lithography process tolerance vary with the width and the shape. Therefore, it is necessary to optimize optical conditions and mask structure so as to prevent displacement over the entire pattern and to ensure lithography process tolerance. For this purpose, by grouping patterns that can be regarded as the same pattern configuration, optimizing optical conditions and mask structure for each group and establishing optical conditions and mask structure satisfying the strictest conditions, optical conditions and mask structure can be optimized for patterns in each group.
According to the invention having the above-summarized structure, by seeking optical conditions and a mask structure capable of limiting displacement of a pattern within a required range, taking manufacturing errors of the mask into consideration, and repeating this procedure until desired exposure tolerance and focal depth are obtained with such optical conditions and mask structure, it is possible to find optical conditions and a mask structure that are optimum to minimize pattern displacement while ensuring lithography process tolerance.
The above and other objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof, which is to be read in connection with the accompanying drawings.